Here is a little visual tut for hemming jeans. Pic#1.. your tools. Pic#2.. determine the length that you want your jeans(I try them on and fold them up to where I like the length.I measure the folded up part in a few spots to determine how much needs to be cut off) and subtract the hem measurement + 1/2 from that measurement. Example the hem on these jeans measured 5/8" . I added 1/2 to be turned under so that equals 1 and 1/8". Cut. Pic#3.. sew 1/2 from raw edge on both pant legs. Pic#4..turn pants inside and press 1/2 right along the stitching. Pic#5.. fold up 5/8" using your little ruler and press and pin. Make sure you place pins so they well be easy to remove as you sew.(It's not really good for your machine to sew over pins). You are now ready to sew. Pic#6..I use my presser foot as a guide. There is a little line on the foot to mark where the needle will sew. I put this a little less than 1/8" from the folded hem edge. I start to sew at a point near the inner leg seam so it doesn't show. Pic#7.. when I sew up to the next seam.. right as the tip of the presser foot meets the seam edge I lift my presser foot and slid the jean-a-ma-jig thingy under the presser foot from the back and put the presser foot back down. Now it will sew nice and smoothly over the thickest part of the seam. Go slow. The Jean-a-ma-jig will just pop off the back and you can keep on sewing until you get to the last seam and repeat the process. Pic#8 .. Ta da.. you are finished.
Other helpful hints. My machine has a sleeve arm that is great for heming sleeves and pants. I use a little sleeve ironing board for pressing and a steam iron for the last pressing.I use a needle especially for jeans or denim and thread as close to the color of the original hem that I can get...(click on the pics to make them big) [wink]